The present invention relates to a drive mode switching device for a motorcycle having a sub throttle valve in addition to a main throttle valve.
In the past, in a motorcycle that requires high-power engine characteristics, an amount of air intake for a high-rpm and high-power engine was ensured, for example, by enlarging a bore diameter of a throttle body. However, in a low-rpm area of an engine, a throttle valve may not be fully opened to a necessary degree to ensure a power or a situation that a sufficient flow rate of air intake may not be ensured when the throttle valve is too much opened. For this reason, in order to prevent the above-described problems, a related-art motorcycle has a sub throttle valve that is opened or closed by an electric actuator as well as a main throttle valve that is driven by a throttle wire (for example, see Patent Documents 1 and 2).
In such a related-art motorcycle, a motion of a throttle grip that is operated by a rider is transmitted to a driving unit of the main throttle valve via the throttle wire, and then the main throttle valve is opened or closed depending on the motion of the throttle grip. Additionally, a driving force of an actuator using a stepping motor or the like is transmitted to a driving unit of the sub throttle valve and an opening degree of the sub throttle valve is configured to be set on the basis of an opening degree of the main throttle valve. In a low-rpm area in which a flow rate of air intake is slow, even when the main throttle valve is fully opened, a sufficient flow rate of air intake is ensured by closing the sub throttle valve. On the other hand, in a high-rpm area, a power is ensured by controlling the opening degree of the sub throttle valve to be larger than that of the main throttle valve.    Patent Document 1: Japanese Patent Publication No. 2001-263186A    Patent Document 2: Japanese Patent Publication No. 2005-273574A
However, in the related-art motorcycle, since a variation rate of the engine power increases in accordance with an amount of a throttle operation (that is, a variation rate of the opening degree of the throttle valve) that is operated by a rider, the engine rpm considerably varies even when the throttle valve is opened to a low opening degree. As a result, a problem arises in that it is not easy for the rider to operate the throttle valve when driving in rain or on a rough road.